Over the past seven years of NIH support, the UCSF Osteoporosis Research Group in the Department of Radiology has developed, tested, and refined the non-invasive technique for vertebral mineral quantification by computed tomography. With this established history of technical development and clinical application, we propose to launch 4 new projects employing the NIH Competing Continuation mechanism. Our overall goal is to define and disseminate information regarding the characteristics of different CT scanner systems as well as develop and apply a new technique for bone mineral assessment at the hip. These goals will be accomplished over a 4 year duration via 2 technical studies commencing in the initial year of funding and 2 pilot clinical trials beginning in the second year. Technical Study #1 proposes to determine the characteristics of CT scanner systems that contribute to errors in quantitative measurements. Its successful completion will allow not only for the identification and quantification of sources of individual machine errors but will, more importantly, provide researchers and clinicians with inter- and intra-scanner correction schemes as a means of normalizing data generated on different systems. Technical Study #2 develops a technique for the non-invasive assessment of bone mineral at the hip using quantitative computed tomography (QCT). Given the widespread concern about hip fracture and the disputatious dialogue surrounding the role of bone mass in these fractures, the development of a technique that sensitively assesses bone mineral selectively at disparate skeletal envelopes will substantially enhance our ability to understand the etiology of fracture at this site. Clinical Trial #1 will compare different methods of bone mineral assessment, including hip QCT, in the setting of hip fracture. We will learn whether hip QCT, with its ability to selectively quantify bone mineral, has superior ability over competing modalities to discriminate fracture cases from controls. Clinical Trial #2 tests the ability of hip and spine QCT to monitor rapid trabecular and cortical bone losses in patients with acute spinal cord injuries. This investigation will be the first of its kind to chronicle bone loss, from these important clinical sites, in a unique subject population at increased risk for the development of osteoporotic fractures.